Electric amplifier control



March 8, 1960 Ni H. YOUNG, JR 2,928,051

ELECTRIC AMPLIFIER CONTROL Filed Sept. l2, 195'? 3 OUTPUT I "HF :zig u a m I sckff/v #orf/.17ML

A llorney 2,928,051 Ennemi' C minimun com 'oL Norman Yanng,uir.,' Niifiey, NJ., yasignar te' -ime'rl `national Telephone and Telegraph CorpratomNutley', NJ., a corporation of Maryland Y. Y 1

Apparition Lseptember iz., iasnseriai Nazs'ssgs'ss z clams.` (Creatif-128) This invention relates "to 'anfelectronic amplifier control circuit.. 4 i y i i `1`n 'radio frequency power aiiipliiie'rs lwhich are used over aj wide range of fret'luncie's,v itis normalffor the amount of Idrive to the -control grid )of the 4finalstage jto vary from frequency to frequency 'within the' band. This variation is oftenundesirabla'since low amounts of 'drive will produce less than "normalout'put and, lwhen using a tetrode or other multi-griddevices -for a final amplifiertube, high amounts of drive' will result inl excessivescreen current and damage to the tube.v Y The ,consideration of excessive screen current and'the'resulting tubedamage very ofterif gives Vris'e to a'liinitation on the circuit output.

For example, mostv circuits inwhich modern power. tubes are used are limited by'tlie'critial value tof screenpow'er dissipation. :At a fixed Screen 'siipplS/"voltage,thisjliriiit may be established at a known value o'f screen current.

There has been some attempt to adapt the screen current as a controlling parameter. Relays haveberi employed which are energized by the screen current, operi-` instead of providing for a continuously variable control.

While utilization ,o'f screen current as a means' of controlling the amount of excitation toa final amplifier tube invention 2 2,928,051 iii-atenei; Mai. dass s'gurbemg ,v i. o ing to'aselect'ed'electrode of `vtheampli'er of Vsaid .particw larstagfe. i i z Y i' Another feat/'ure inconiu'i'iction themain feature above :is l'the lp'r'vision 4of a fsaturabley "1'. torv coupledto'be responsive tothe above-meuf ned and Ihaving lits output coupled tofthe "bo ,-mA tio .gnfrllblfvbl'fsge @amelie/previ@ a maar@ e @si the fontiri s'variablecoiitrol of th'evoltage source@ The `tor' oing and :otherT objects fand features of this the manner of a,t t`aining will become more napparent andthe inveiitionitfself 'polpetter un' dersto'od by reference to the following "descripfon v-ofjan einbodirnentof the invention taken conjunction with the accompanying drawing :the ligure Vis 'a schematic circuit'and'bloclcA diagram Showing two stages of a multi-stage amplifier arrangement 'controlled through a saturable reactor. u'. l Y *Y ,In the igur'ef-the .(radiotrequency) signal vto, be

represented by Atetrode`18.

i y which it is unsafe to operate Vthe tube, and thecore of currenttlowing through the winding 28, the impedanceV or to any particular stage tube of a multi-stageamplifier,A l

arrangement is desirable, one drawback to a simple solu-V tion of this nature is the fact that the controlling phenomeon is a current rather than a voltage. This current, furthermore, may be measured only at a point having potential far from ground; While an easy means to effect a control for a particular stage is by changing the bias applied to the control grid of a preceding amplifier stage, there is requisite a means for translating this changing screen current to a varying voltage value .to obtain the proper control. In addition, `freedom to connect thev positive terminal of this varying voltage source to ground or to any desired reference bias is essential.

It is therefore an object of the present invention to pro# vide an improved amplifier control arrangement.

It is a further object of the present invention toproV vide an amplifier control arrangement which will not *l have the inherent disadvantages that accompanying mevstage in proportion to thecurletlt flowing to .a particular electrode.

, ing and the lD.C. winding which-would prevent the 63A the saturable reactor 20 Vis designed such that saturation is attained when the screen grid current is closeto said value, such as for example about percent. yS'nunting devices' may be used to adjust the saturation characteiistics of the saturable reactor if necessary. The A.C. (alternating current) winding 21 is placed in series withv the fprimary winding 22 of a second transformer 23. Both o'f the windingsy 21 and 22V are connected to any conven-v ient A.C. voltage source, such as a 60 cycle supply 24. The output from the secondary 25 of the'transformer 23 is rectified by the diode 26 and passed to the load circuit 27 which'actsas an averaging or integrating means. As saturationof the core is approached by the screen grid of winding 21 for the 60 cycle current gradually approaches a value much smaller than the Vprimary mpedance of @transformer 23. The diminution of the impedance factor of the coil 21 allows a larger current flow i through the transformer primary winding 22 and hence induces a larger voltage in the secondary25. Ak larger current iiow around the secondary lo'op through the diode 26 and theload circuit 27 causes thepotential at point 29 to become more negative.` Obviously, the more negative the potential at 29, the ymore negative will be the `potential of the grid 12 and hence a reduction in the positive gain at anode 14. VVVConversely, it follows that a small screen current flow through the winding 28 will result in a small induced current at 25 and hence the point 29 and the grid 12 will move in a positive direction toward ground l potential causing a relativelyA large gainat the anode 14.

As is well known, in saturable reactor devices therer is a minimum of inductivecoupling between the A.C; wind cycle power from producing a hum on the amplifier 1E. In` the preferred embodiment av saturable reactor in -i'combination with a second transformer is used as the control means. Other switching-'devices might be used, such as a relay, to either cause a predetermined lower potential to be applied to the grid 12 orto cause the oiit cur., ,nt

put from 14 to be interrupted. The variable voltage available at 29 may be used in a variety of ways to control the gain of amplifier stages or the loss introduced by attenuation in the signal. The embodiment shown is preferred because the limitation to the lower stage is not abrupt as with a relay device which often gives rise to erratic control and spurious signals and would require filtering components to compensate for the spurious signals. As mentioned above a relay arrangement would limit operating the system close to maximum output, give a period of non operation and has a mechanical movement time delay. The saturable reactor provides an isolation device as well as a sensing device.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is lmade only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

I claim:

1. A control system in a multi-stage electronic amplifier arrangement comprising at least first and second tetrode tubes, first and second frequency resonant circuits respectively coupled to the anodes of said first and second tetrode, a saturable reactor, a transformer, circuitnI means coupling the screen grid of said first tetrode to a first winding of said saturable reactor, and an alternating current kvoltage source coupled in series to a second winding of said saturable reactor and a first winding of said transformer, a second winding of said transformer series 30 coupled to a rectifier means and a load device, the control grid of said second tetrode series coupled through said load device to a first reference potential, the screengrid and the cathode element of said second tetrode series coupled through an impedance circuitry to said first reference potential, a voltage source coupled to the control grid of said second tetrode to provide excitation thereto, circuitry means coupling the anode of said second tetrode to the control grid of said first tetrode to provide excitation thereto in accordance with the output therefrom.

2. A control system in a multi-stage electronic amplifier arrangement comprising at least first and second tetrode tubes, a saturable reactor, a transformer, circuitry means coupling the screen grid of said first tetrode to a first winding of said saturable reactor, and an alternating current voltage source coupled in series to' a second Winding of said saturable reactor and a first winding of said transformer, a second WindingV of said transformer series coupled to a rectifier means and a load device, the control grid of said second tetrode series coupled through said load device to a first reference potential, the screen grid and the cathode element of said second tetrode series coupled through an impedance circuitry to said first reference potential, a Ivoltage source coupled to' the control grid of said second tetrode to provide excitation thereto, circuitry means coupling the anode of said second tetrode to the control grid of said rst tetrode to provide excitation thereto in accordance with the output therefrom.

References Cited in the tile of this patent UNITED STATES PATENTS 2,615,977 Sziklai et al. Oct. 28, 1952 2,662,125 Stafford Dec. 8, 1953 2,694,114 Kalfaian Nov. 9, 1954 2,703,825 Macdonald Mar. 8, 1955 

